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    <title>promise对象的all方法</title>
    <meta name='viewport' content='width=device-width, initial-scale=1'>
    <link rel='stylesheet' type='text/css' media='screen' href='main.css'>
    <script src='main.js'></script>
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<script>
// Promise.all()将多个promise的实例合并成一个新实例
// 只有当所有的promise实例的状态都为fulfilled,最终的结果才能执行.then
// 只要有一个promise实例的状态为rejected,那么最终的结果会执行.catch
    let promise1=new Promise((resolve,reject)=>{
        setTimeout(()=>{
            resolve(1000)
        },1000)
    })
    let promise2=new Promise((resolve,reject)=>{
        setTimeout(()=>{
            resolve('hello')
        },1000)
    })
    let promise3=new Promise((resolve,reject)=>{
        setTimeout(()=>{
            resolve('hhhh')
        },1000)
    })
    let promise4 = Promise.all([promise1,promise2,promise3])
    .then(res=>{
        console.log(res);
    })
    .catch(err=>{
        console.log(err);
    })
    

</script>
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